JPH0353875Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Technical Field of the Invention) The present invention relates to heat-shrinkable rubber and plastic covering materials used for waterproofing, corrosion protection, etc. of connections of electric cables, anticorrosive steel pipes, etc.

(Conventional technology) Tubes made of heat-shrinkable rubber and plastic;
Covering materials such as sheets are used to waterproof and protect the joints of power cables, communication cables, anti-corrosion coated steel pipes, etc.
It is widely used for corrosion prevention purposes. It is necessary to provide an adhesive layer on the inner surface of these heat-shrinkable rubber and plastic tubes, and this adhesive is of the adhesive type or hot-melt type, but both types of adhesive are used to shrink the heat-shrinkable tube. When heated, it softens, flows, and adheres to the covered part.

The degree of heating during construction is regulated by the softening temperature of the adhesive used.

In particular, in the case of a hot-melt adhesive layer, sufficient adhesive strength cannot be obtained below the softening point, so a considerably high bonding temperature above the softening point is required.

However, in most cases, the covered part is preheated or heated to shrink by moving a local fire source such as a hand gas burner.

For example, if the construction site is a narrow place such as a manhole, the temperature distribution of the sheathed part tends to be uneven, and if the sheathed part has a wide area such as a large diameter pipe, the part that is hit by the flame will be heated. However, since other parts are left to cool, the temperature distribution of the covered part becomes quite wide.

For this reason, when all parts of the covered part are heated to the temperature necessary to obtain sufficient adhesion, the temperature locally becomes quite high. The temperature distribution at this time is usually 120℃, although there are exceptions due to work conditions etc.
A temperature of ~150°C is said to be common. Therefore, when selecting the adhesive itself, rubber-based adhesives are often used so that they can adhere sufficiently even in the low temperature range, especially when there are variations in the heating of the covered part.

The reason for this is that since it is based on rubber and contains various tackifiers, the viscosity changes little with changes in temperature, so it can be applied satisfactorily even when there are variations in application temperature.

However, a drawback of such adhesives is that they have low adhesive strength.

In addition, hot-melt type adhesives are sometimes used to compensate for this drawback of low adhesive strength, but in this case, the viscosity of hot-melt type adhesives decreases rapidly when the temperature rises above the softening point. For this reason, if you use an adhesive with a low softening point to ensure sufficient adhesion even in low-temperature areas where the temperature of the covered area varies, the fluidity of the adhesive will increase even more in high-temperature areas, and the shrinkage force of the shrink tube will cause the adhesive to bond. The adhesive layer is extruded and the adhesive layer in this area becomes extremely thin, which has the disadvantage that sufficient adhesion and waterproofness cannot be ensured against heat cycles and the like during use after construction.

(Purpose of the invention) As a result of careful consideration of the above-mentioned reality, the present invention has been developed to ensure a sufficient adhesive layer thickness within the range of practical construction conditions, and to ensure that the adhesive layer is sufficiently thick under the usage conditions such as heat cycles. Heat-shrinkable rubber that exhibits sufficient properties in
A plastic covering is provided.

(Summary of the invention) The present invention has been made as a result of intensive study on the relationship between the thickness of the adhesive layer and the adhesive strength of the conventional covering material of this type, and it has been confirmed that the result is as shown in FIG. Further, although the attained adhesive strength S ₁ differs slightly depending on the type of adhesive, when the adhesive layer thickness is 0.6 mm or less, the adhesive strength tends to decrease as the adhesive layer becomes thinner.

In addition, when using such heat-shrinkable rubber and plastic tubes, it is unavoidable that they undergo heat cycles during use, and it is necessary to maintain sufficient adhesion and waterproofness against these heat cycles. Although this is an important characteristic, the thickness of the adhesive layer is also very relevant in this case, and it has been found that heat cycle resistance is good if the thickness is 0.5 mm or more. The reason for this is not clear, but it is thought to be as follows.During the heat cycle, heat-shrinkable rubber and plastic tubes are made of plastic materials, while sheathing parts are made of metal such as pipes, so the mutual thermal expansion occurs. When the temperature increases and decreases during heat cycles, strain due to the difference in thermal expansion is applied to the adhesive layer, resulting in stress that shifts the adhesive interface, making the adhesive layer more likely to be destroyed. In this case, if the adhesive layer has a suitable thickness or more,
It is assumed that the stress that causes the adhesive interface to shift is reduced by the adhesive layer absorbing and relaxing the stress, which, combined with the above-mentioned stronger adhesive force, makes it more resistant to heat cycles. .

Furthermore, when a heat-shrinkable rubber, plastic sheet, or tube is attached to a covered portion and heated, it contracts in the radial direction, and at this time its wall thickness increases. The thickness of the adhesive layer located in the inner layer also increases. Generally, the heat-shrinkable rubber or plastic used as the base material has a shrinkage rate of about 50%, so the wall thickness will approximately double after construction. In other words, it was found that if the adhesive layer is not to be washed away, a thickness of 0.25 mm or more is required in the unshrinked state.

The present invention is based on the above-mentioned knowledge, and as a result of further intensive studies, we have developed a covering material made of heat-shrinkable rubber and plastic that has a function capable of achieving the intended purpose.

The heat-shrinkable rubber or plastic covering material of the present invention will be explained with reference to the drawings. As shown in Figs. (inner surface for tubes, one side for sheets)
In a heat-shrinkable rubber or plastic covering material provided with an adhesive layer 2, an adhesive layer 2' having a softening point of 130° C. or higher is placed on the adhesive layer 2' on the base material side. It is characterized by having a two-layer structure including an adhesive layer 2'' whose temperature is below 120°C.

Although the adhesive used in the present invention is not specified at all, in consideration of ease of handling in actual use, it is preferable to use a hot melt type adhesive for any adhesive.

(Example of idea) The present invention will be specifically explained below using examples.

Example 1 Melt index 1.0 and density 0.92 as base material
Low-density polyethylene mixed with 2.5% carbon and cross-linked to give it heat-shrinkability, inner diameter with a shrinkage rate of 50%.
A heat-shrinkable tube with a diameter of 600 mm and a wall thickness of 1 mm is used, and terpene phenol resin (YS Resin PX2130 (manufactured by Cheap Crude Oil)) is mixed into the inner surface of the tube with ethylene/vinyl acetate copolymer (Evaflex 150 (manufactured by Mitsui Polychemicals)). A 0.5 mm thick sheet of hot-melt adhesive with a softening point of 133°C was provided, and the inner surface was coated with ethylene-vinyl acetate copolymer (Evaflex 150) and Alcon P100.
(Arakawa Chemical's tackifier resin), microcrystalline wax (Toyo Petrolite), and a hot melt adhesive with a softening point of 110℃ prepared by mixing carbon for coloring into a 0.3 mm thick sheet. A heat shrinkable tube with a laminated adhesive layer was obtained.

This heat-shrinkable tube was used to heat-shrink the welded joint of a 400A polyethylene-coated steel pipe after preheating it with a hand gas burner. At this time, the low temperature part of the pipe was 120°C, and the high temperature part was 150°C.

When the anti-corrosion coating made from the heat-shrinkable tube thus prepared was heat cycled 50 times between 80°C and -30°C and then immersed in water, an insulation resistance test was conducted, and there was no decrease in insulation resistance, indicating good waterproofing. It was found that anti-corrosion performance was maintained.

Furthermore, when the heat shrink tube was disassembled after the heat cycle evaluation test, a low softening point adhesive layer remained in the area where the preheating temperature was 120°C to 130°C.
In the area between 140°C and 150°C, the adhesive layer with a low softening point was washed away and almost nothing remained, but the adhesive layer with a high softening point was firmly adhered.

Example 2 A polyamide hot melt adhesive with a softening point of 140°C (Barsalon 1140 (manufactured by Henkel Japan)) with a thickness of 0.5 mm was applied as an adhesive layer with a high softening point on the inner surface of the base heat-shrinkable tube similar to that in Example 1. As in Example 1, a heat-shrinkable tube was prepared with a polyamide hot melt adhesive (Versamide 930 (manufactured by Henkel Japan)) with a softening point of 110°C at a thickness of 0.5 mm on the inner surface as an adhesive layer with a low softening point. The anti-corrosion coating was created by preheating and shrinking with a hand gas burner.

The preheating temperature of the pipe at this time was 120°C in the low temperature section and 140°C in the high temperature section.

This anti-corrosion coating was heated to 80°C to -30°C in the same way as in Example 1.
When heat cycled at ℃ and conducted an insulation resistance test, the insulation resistance did not decrease at all, indicating good waterproofing and
It was found that the anti-corrosion performance was maintained.

When the sample was disassembled after the test, Versamide 930 was glued to the low temperature part, but Versamide 930 was glued to the high temperature part.
930 was washed away and very little remained, but Bar Salon 1140 was not washed away at all and was firmly attached.

As can be seen from the above examples, the areas where the preheating temperature is low are sufficiently bonded by the adhesive layer with a low softening point on the inner surface, while the areas where the preheating temperature is high are such that the viscosity of the adhesive layer with a low softening point decreases and the heat shrinkable tube Although it had been extruded by the shrinkage force and was considerably washed away, the adhesive layer with a high softening point had sufficient adhesion and the adhesive layer thickness and adhesive strength were ensured to withstand heat cycles.

Comparative Example 1 A heat-shrinkable tube having a thickness of 1 mm of Versamide 930 with a softening point of 110°C of Example 2 was provided on the inner layer of the heat-shrinkable tube as a base material similar to that of Example 1.
As in 2, it was preheated and shrunk using a hand gas burner (Figure 2).

The temperature distribution of the pipe at this time was 120°C to 140°C, which was almost the same as in the example.

The anti-corrosion coating thus created was 80 mm as in the example.
After conducting a heat cycle test from ℃ to -30℃, the insulation resistance of the anti-corrosion coated joint was examined by immersing it in water as in the example. After 30 cycles, the insulation resistance of the coating was abnormally reduced to 400Ω. Ta.

When the coating is dismantled after the insulation resistance test, the preheating temperature
In the areas where the temperature was low (120°C to 125°C), the adhesive layer did not wash away and was firmly adhered, but the preheating temperature was 130°C to 140°C.
The adhesive layer is very thin in the areas where the temperature is high, and the adhesive strength is very low in these areas, and there are some areas that are not bonded and water infiltration is observed, which reduces the waterproof performance of the anti-corrosion coating. This is thought to have caused the insulation resistance to decrease.

Comparative Example 2 An adhesive layer of the polyamide hot melt adhesive (Barsalon 1140) with a softening point of 140°C used in Example 2 was provided on the inner layer of the base heat-shrinkable tube similar to Example 1 to a thickness of 1 mm. The heat-shrinkable tube was preheated and shrunk using a hand gas burner in the same manner as in the example.

The temperature distribution of the pipe at this time was 120°C to 150°C. This anti-corrosion coating was heated at 80°C to - as in the example.
After conducting a heat cycle test at 30°C, the insulation resistance was examined by immersing it in water. After 20 cycles, the insulation resistance of the coated portion had decreased to 300Ω.

When this coating was dismantled and investigated, the adhesive layer covered all parts and did not wash away, but there was no adhesive at all in areas where the preheating temperature was low, at 120°C to 135°C, and water infiltration was observed. It was found that the insulation resistance decreased because of this.

(Effect of the invention) As can be seen from the above examples and comparative examples,
Although heat-shrinkable tubes and sheets are often used for waterproofing and anti-corrosion purposes, hand gas burners are often used due to their ease of construction, and in this case, they are bonded using an adhesive layer. Therefore, preheating of the substrate is essential, and it is very difficult to heat the entire surface uniformly and evenly using local heating methods such as hand gas burners, which may limit the use of heat-shrinkable covering materials. The product of the present invention has sufficient adaptability to practical heating unevenness, and its practical value is extremely large.

[Brief explanation of the drawing]

FIG. 1 is a curve showing the relationship between adhesive layer thickness and adhesive strength. Furthermore, FIGS. 2 and 3 are explanatory cross-sectional views showing one embodiment of the heat-shrinkable rubber and plastic covering material of the present invention. 1... Base material of heat-shrinkable rubber, plastic molded body, 2'... Adhesive layer with a softening point of 130°C or higher,
2″…Adhesive layer with a softening point of 120°C or less.

Claims (1)

[Claims for Utility Model Registration] (1) In a covering material such as a tube or sheet made of heat-shrinkable rubber or plastic, in which an adhesive layer is provided on one side of a base material, the adhesive layer is provided on the side of the base material. A covering material made of heat-shrinkable rubber or plastic, characterized by having a two-layer structure: an adhesive layer with a softening point of 130°C or higher, and an adhesive layer on the adhesive layer with a softening point of 120°C or lower. (2) The heat-shrinkable rubber or plastic covering material according to claim 1, wherein each adhesive layer is a hot-melt adhesive layer. (3) The heat-shrinkable rubber made of plastic according to claim 1 of the utility model registration claim, characterized in that the thickness of the adhesive layer with a softening point of 130° C. or higher in contact with the base material is at least 0.25 mm. Covering material.